1. Field of the Invention
The present invention relates to a driving apparatus for moving an optical lens in a direction of an optical axis thereof. More particularly, the present invention relates to a driving apparatus constructed of an electromechanical transducing actuator using an electromechanical transducer such as a piezoelectric element, an electrostrictive element, and a magnetostrictive element.
2. Description of Related Art
As a driving apparatus, there has been used an electromechanical transducing actuator for moving a movable unit by utilizing an electromechanical transducer such as a piezoelectric element, an electrostrictive element, or a magnetostrictive element. For example, precision equipment such as a camera, a DVD player, a CD player, an MD player, and an endoscope needs a driving apparatus for moving an optical lens in an optical axis direction. Used as this driving apparatus is the electromechanical transducing actuator. Such driving apparatus constructed of the electromechanical transducing actuator includes a driving apparatus arranged such that a fixed member is fixed to one end of the piezoelectric element or the like while a friction drive shaft is fixed to the other end, and a movable body is frictionally connected to the friction drive shaft. In this driving apparatus, the movable body is pressed against the friction drive shaft by an elastic force of an elastic body for ensuring the frictional connection between the movable body and the friction drive shaft.
Conventionally used as the elastic body for pressing the movable body against the friction drive shaft are a leaf spring, a coil spring, and the like. For example, EP 0 675 589 discloses, in FIG. 18, a leaf spring secured by screws so that a friction drive shaft is interposed between the leaf spring and a movable body. This is arranged to frictionally connect the movable body to the friction drive shaft. In another example, U.S. Pat. No. 6,188,161 has proposed a driving apparatus structured such that a friction drive shaft is grasped by a leaf spring of a complicated shape as shown in FIGS. 10 to 12.
In a compact camera used in for example a cellular phone, however, the movable body such as an optical lens is small in size. This makes it difficult to secure the leaf spring by the screws as described in EP '589. As the spring is reduced in size, a spring constant becomes larger, so that such small springs would be more susceptible to errors caused at the time of manufacture. Consequently, the leaf spring of the complicated shape in the driving apparatus disclosed in U.S. Pat. No. '161 is hard to manufacture. Further, the small spring with a large spring constant would cause deterioration in mounting workability. If such spring is forcedly mounted, the spring would receive excessive force. This may cause plastic deformation of the spring during a mounting work. In this case, the elastic force of the spring would decrease and accordingly the movable body could not obtain a sufficient frictional force.